1. Field of the Invention
The present invention relates to a fingerprint sensor, especially to a sensing method and circuit of a fingerprint sensor.
2. Description of the Prior Arts
With reference to FIGS. 12 and 13, a schematic diagram of a projected capacitive fingerprint sensor 50 is shown. The projected capacitive fingerprint sensor 50 has multiple electrode plates 51 arranged in a matrix, a protection electrode 52 and a sensing circuit 53 connected to the electrode plates 51. The sensing circuit 53 is used to detect a capacitance value of a capacitor formed between the finger 60 and each electrode plate 51, such as a capacitor CSA between the finger 60 and the electrode plate (Plate A). According to the capacitance value of the capacitor formed between the finger 60 and each electrode plate 51, a fingerprint image of the finger can be obtained. However, a measurement result of the capacitance value of the capacitor formed between the finger 60 and the electrode plate 51 is affected by other factors. For example, when detecting the electrode plate (Plate A), multiple capacitors respectively formed between the electrode plate (Plate A) and other electrode plates (Plate B˜Plate D) around the electrode plate (Plate A), and a capacitor CFAS formed between the electrode plate (Plate A) and the protection electrode 52 (such as an electrostatic discharge protection electrode) also affect the measurement result.